Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-11-04
2004-11-23
Thompson, Craig (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
Reexamination Certificate
active
06822299
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of semiconductor device fabrication, and more particularly to methods for making conductive contacts in the formation of a semiconductor device.
BACKGROUND OF THE INVENTION
As semiconductor fabrication moves toward maximizing circuit density, electrical components are formed at a number of layers and different locations. This requires electrical connection between metal layers or other conductive layers at different elevations in the substrate. Such interconnections are typically provided by forming a contact opening through insulating layer to the underlying conductive feature. With increasing circuit density, the dimensions of openings for electrical contacts become narrower and deeper, posing a challenge to provide adequate conductive fill within high aspect ratio openings.
Typically, in forming a contact plug, a thin layer of titanium is deposited over the top of a silicon base layer (substrate), and tungsten or other electrically conductive plug material is then deposited from tungsten hexafluoride (WF
6
) by chemical vapor deposition (CVD) to fill the contact hole. However, there are several limitations of tungsten (W) plugs. Tungsten does not provide an adequate fill for high aspect ratio features. In addition, the use of WF
6
as a precursor gas in the formation of tungsten plugs, can result in the penetration of the fluoride component into the adjacent dielectric layer causing lateral encroachment and wormholes.
Titanium nitride (TiN) films have attractive properties that may overcome the limitations of tungsten plugs as integrated circuit (IC) devices continue to shrink below 0.15 micron dimension. TiN films have been deposited by low pressure chemical vapor deposition (LPCVD) using tetrakisdimethyl-amidotitanium (TDMAT) and ammonia as precursor gases. However, TDMAT films have a high carbon content and when subjected to high temperatures in the presence of oxygen, become porous and, therefore, are unusable as a conductive contact.
TiN films and liners have also been deposited from titanium tetrachloride (TiCl
4
) and ammonia (NH
3
) by CVD onto a titanium (Ti) liner overlying the insulative layer. Although useful for forming a thin liner, when pure TiCl
4
-based TiN is deposited to fill a via or other contact opening, the material does not adhere well to the Ti thin layer, particularly when the TiN layer becomes greater than about 150 to about 200 angstroms thick.
Therefore, it would be desirable to provide a titanium nitride material that can be used as a replacement fill material for tungsten in forming conductive contacts in high aspect ratio features in a semiconductor device.
SUMMARY OF THE INVENTION
The present invention provides methods for forming conductive contacts in the construction of semiconductive devices, and the conductive components formed by those methods. The method is useful for fabricating contacts to electrical components beneath an insulation layer in an integrated circuit such as memory devices.
The present TiCl
4
-based titanium nitride films are particularly useful as conductive contacts to replace tungsten (W) plugs in high aspect ratio features, particularly openings and other features having an aspect ratio of 3:1 or greater. The films also overcome inadequacies of pure TiCl
4
-based titanium nitride films that are used as fill material for forming conductive contacts or interconnects within contact openings formed through an insulative layer of a semiconductor structure. Pure TiCl
4
-based titanium nitride fills do not adhere well to the surface of insulative sidewalls of a contact opening, and can also cause the insulative layer to crack due, at least in part, to the pressure exerted when the thickness of the fill within the contact opening is about 200 angstroms or greater.
The present invention overcomes the problems of a pure TiCl
4
-based titanium nitride plugs or barrier film by incorporating diborane (B
2
H
6
) into the gas mixture to dope the TiCl
4
-based titanium nitride film during the deposition process. The addition of B
2
H
6
to the precursor gas used to form the TiCl
4
-based titanium nitride film has been found to improve the mechanical properties of the resulting titanium nitride film with substantially no impact on its conductive properties. In particular, the gaseous mixture used to form the boron-doped, titanium nitride contacts comprises diborane (B
2
H
6
) in an amount effective to provide a contact having an amount of boron to provide a level of adhesion of the conductive contact to the insulative sidewalls of the contact opening to substantially eliminate peeling of the contact from the sidewalls and cracking of the body of the insulative layer. The mixture further includes an amount of ammonia (NH
3
) to provide the contact with a level of nitrogen effective to maintain the conductivity of the contact at a predetermined level for an effective electrical contact with a conductive or active area within the substrate to/from an active area within a semiconductor device and/or a memory or logic array.
In one aspect, the invention provides methods for forming a titanium nitride conductive contact in a via or other contact opening of a semiconductor structure. The opening is formed through an insulative layer to a conductive area, such as a source/drain region, in an underlying silicon substrate. The method is particularly useful for forming conductive contacts within vias and other openings having an aspect ratio of about 3:1 or greater, and a width dimension of about 0.25 &mgr;m or less.
According to one embodiment of the method of the invention, a titanium nitride conductive contact is formed by first depositing a seed layer comprising titanium silicide (TiSi
x
) over the silicon substrate at the bottom of the contact opening, preferably to a thickness of about 250 to about 300 angstroms. Preferably, the TiSi
x
seed layer is deposited from titanium tetrachloride (TiCl
4
) and hydrogen (H
2
) by plasma-enhanced chemical vapor deposition (PECVD).
A boron-doped titanium nitride film (i.e., titanium boronitride, TiB
x
N
y
) is then deposited onto the seed layer to fill the contact opening, typically to a thickness of about 1000 to about 3000 angstroms. Preferably, the TiB
x
N
y
layer is deposited from a gas mixture of TiCl
4
, NH
3
, B
2
H
6
, and one or more carrier gases, by thermal CVD at a pressure of about 1 to about 15 Torr and a temperature of about 550 to about 700° C. The substrate can then be processed to remove excess material, for example, by chemical-mechanical polishing, to form the conductive contact in the opening.
In another embodiment of the method of the invention, a multi-layered titanium nitride conductive contact is formed within a contact opening of a semiconductive structure. A titanium silicide seed layer is first formed over the silicon substrate at the bottom of the contact opening. To form the layered contact, alternating layers of titanium nitride and boron-doped titanium nitride are then deposited over the seed layer. In forming the alternating layers, a layer comprising titanium nitride (undoped) can be deposited from a first gaseous mixture comprising TiCl
4
and NH
3
, to form a layer typically about 100 to about 500 angstroms thick. Diborane (B
2
H
6
) can then be introduced into the gaseous mixture to deposit an intermediate layer of boron-doped titanium nitride to form a layer typically about 100 to about 500 angstroms thick. The flow of diborane into the gas mixture can then be stopped to deposit a next layer of titanium nitride layer that is not doped to a typical thickness of about 100 to about 500 angstroms. Additional alternating layers of doped and undoped titanium nitride can be deposited to fill the opening, with the uppermost layer being undoped titanium nitride.
Another aspect of the invention is a conductive contact formed in a semiconductor structure of a semiconductor circuit. The semiconductor structure comprises a silicon substrate, an overlying insulative layer, a contact opening formed through the
Castrovillo Paul
Derraa Ammar
Sharan Sujit
Micro)n Technology, Inc.
Thompson Craig
Whyte Hirschboeck Dudek SC
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